The present invention relates to a stereomicroscope having parallel conducted observation channels behind the objective assembly.
Two different types of stereomicroscopes are being used today, namely ones having a common main objective for both stereoscopic observation channels, and ones having separate objectives for the two observation channels (Greenough type).
In the first-mentioned type of stereomicroscopes the focal planes for both observation channels coincide, which results in edge-sharp images even in the case of high magnifications. The focal planes of Greenough stereomicroscopes form an angle with each other, which makes this type of microscope unsuitable for the viewing of long flat objects. On the other hand, Greenough microscopes have the advantage of being less expensive to manufacture than stereomicroscopes with common main objectives.
Both types of microscopes also have a number of other advantages and disadvantages as compared with each other. Thus, in the first-mentioned type of microscopes, despite extensive chromatic correction of the main objective, transverse chromatic aberration in the direction of the stereo base occurs, due to the non-concentric passage of the two stereo channels through the objective. This aberration, which in principle does not occur in Greenough stereomicroscopes, noticeably reduces the resolving power of stereomicroscopes having a common main objective. On the other hand, the attachment of accessories to stereomicroscopes of the Greenough type is difficult since the optical axes of the two stereo channels are normally inclined to each other.
From German Utility Model (Gebrauchsmuster) No. 69 26 292, it is known to make the mutually inclined axes of a Greenough stereomicroscope which are inclined to each other parallel by means of a pair of dispersive prisms, as illustrated in FIG. 9 of this Gebrauchsmuster. Further similar pairs of prisms are necessary for each image output in order to eliminate the chromatic aberration introduced by the deflection so that, in the final analysis, the axes of the stereo channels extend parallel to each other only in a small region between the prisms.
U.S. Pat. No. 3,353,892 of Minns and Hopkins, issued Nov. 21, 1967, describes a stereomicroscope having a common main objective in which the transverse chromatic aberration in the direction of the stereo base is compensated for by a pair of deflecting prisms. This microscope has observation channels which are inclined to each other, and thus becomes comparable to a Greenough microscope. The prisms are made of the same glasses as the common main objective. They must have a rather large wedge angle in order just to compensate for the prism effect of the non-concentrically traversed main objective.
The object of the present invention is to provide stereomicroscopes which have stereo axes which extend in parallel behind the objective assembly and in which chromatic aberrations in the objective assembly are corrected, and in which in particular, there is also no substantial chromatic aberration in the direction of the stereo base.